Tim McDonnell

Climate Desk Associate Producer

Tim McDonnell joined Climate Desk after stints at Mother Jones and Sierra magazine. He remains a cheerful guy despite covering climate change all the time. Originally from Tucson, Tim loves tortillas and epic walks.

Yesterday was a good day for the climate movement, as over 300,000 people—according to the event's organizers—descended on Manhattan for the biggest climate change march in history. The record-breaking turnout was a powerful sign that climate change is gaining traction in mainstream consciousness.

But even as the marchers were marching, new science was released that underscores how just how little time the world has left to break its addiction to fossil fuels. Global carbon emissions are the highest they've ever been, and are on the rise, according to a new climate study published in Nature Geoscience over the weekend.

The study totaled global carbon emissions from fossil fuel combustion and cement production—which together account for over 90 percent of total emissions—and found that they rose 2.3 percent in 2013 to their highest level ever recorded, approximately 36.1 metric gigatons.

We'll use up our remaining carbon "budget" in the next 30 years.

Emissions have been on the rise for decades, setting a new record almost every year. The rate of emissions growth has increased since the 1990s—when it was 1 percent per year—to the last decade, when the average annual growth rate has been around 3 percent. The rate of growth in 2013 was actually slower than in 2012, the study found, reflecting energy efficiency improvements in the US and Europe that have reduced the amount of carbon emitted per unit of GDP. But that obscures increasing rates of growth in emissions from China and India. Globally, greenhouse gas emissions are still on pace to trigger what scientists say could be a catastrophic amount of warming, said Pierre Friedlingstein of the University of Exeter, the study's lead author.

"China will be twice as much in 10 years," Friedlingstein said. "We need to change the trend. There's a need to reduce emissions in every country."

Which brings us to the really unsettling part of this report—its attempt to pin down exactly how long we have to make that happen. Climate scientists often talk about a carbon "budget," which is the total cumulative emissions that will lead to a specified level of global warming. To have a better-than-even chance to stay within a 3.6 degree Fahrenheit increase over 1990s temperatures, the international standard for a reasonably safe level of warming, our global carbon budget is 3,200 gigatons. Since the Industrial Revolution, we've used up about two-thirds of that. On our current path, the study finds, we'll use up the rest in just the next 30 years.

In other words, if the emissions trend isn't reversed before 2045, we would have to drop immediately to zero carbon emissions on the first day of 2046. Since an instantaneous gearshift like that is obviously impossible, there's a need to bring emissions under control in the short term. That way we can stretch the "budget" for many more years and not face a choice between catastrophic climate change or a plunge into the Dark Ages.

We'll get an updated sense of how serious world leaders are about that goal at tomorrow's United Nations climate summit, which is meant as a curtain-raiser for major international climate negotiations next year in Paris.

Natural gas can't be a "bridge fuel" unless we crack down on methane leaks, he tells Climate Desk.

Few figures in the climate change debate are as polarizing as former Vice President Al Gore. His fans and his enemies are equally rabid, and his 2006 film An Inconvenient Truth is still probably the most-referenced document on climate change in history. In the last few years, Gore's global warming work has mostly been channeled into a nonprofit he oversees called the Climate Reality Project, which organizes rallies and educational events.

This week, that group held its annual "24 Hours of Reality" marathon of live-streamed videos and appearances by Gore and other celebrities to raise funds for climate action. The event took place in New York City, which is gearing up for a series of meetings and protests in advance of the biggest climate summit of the last five years, to take place Tuesday at the United Nations. Gore took a break from the broadcast to chat with Climate Desk's Inquiring Minds podcast, offering his views on everything from President Obama's climate polices and the role of the tea party in US politics to his hopes for a strong international climate treaty.

Gore said that Obama hasn't yet gone far enough in his efforts against climate change, but that he nonetheless admires "what the president has done."

"In his first term I expressed some considerable concern about what I thought he was failing to do," Gore said, adding that after the demise of cap-and-trade legislation in the Senate, "there was not the kind of energy and activity that I felt was appropriate." But Gore credited Obama for shifting course dramatically in his second term, and for going around the "logjam" in Congress by instructing the EPA to issue "historic regulations" on carbon emissions from power plants.

Gore did criticize some of Obama's policies, including the president's "all-of-the-above" energy strategy, which Gore described as the "prevailing code for 'let's keep burning fossil fuels.'"

"But it's not fair to just take those things out of context without looking at the totality of his policies," he added. "And the totality of what he's doing now in his second term is really historic."

Gore expressed skepticism about the fracking boom. He said he opposed the use of natural gas as a bridge fuel—something the Obama administration has supported—"until and unless they demonstrate the ability to stop the methane leaks at every stage of the process, particularly during fracking." (Methane is a powerful greenhouse gas that some scientists argue can negate the climate benefits of burning natural gas instead of coal.) And he added that the increasing cost-effectiveness of solar and wind power was already posing a "threat to the viability of natural gas as a source of energy in the marketplace."

You can hear Gore's comments in full on this week's episode of our Inquiring Minds podcast, below, and see the highlights of his comments in our exclusive video above.

But the week's main event is on Tuesday at the United Nations, where Secretary-General Ban Ki-moon will preside over a confab of heads of state (including President Obama), diplomats, CEOs, and policy wonks who will all be talking about how to prevent global warming from reaching catastrophic levels.

The UN conference is meant as a preparation for the major international climate negotiations scheduled for next winter in Paris, a summit that is theoretically intended to produce an aggressive carbon-cutting treaty to replace the Kyoto Protocol. In other words, in classic UN fashion, it's a meeting about a meeting, or as Mashable's Andrew Freedman more eloquently put it, "the cocktail party ahead of a formal dinner." So it's probably safe to assume that next week we'll be served appetizers and amuse-bouches rather than a substantive meal, climate action-wise.

Still, New York is a city on the front lines of climate change: Just yesterday the last subway line damaged two years ago by Hurricane Sandy finally came back online. So the excitement is building. Here are a few things to look for: